US Military's Skin Sensors Could Reveal Science of Sweat

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Blood tests may be the current standard method of tracking
certain indicators of a person's health, but a new project led by
the U.S. military could change the way health is monitored.

It turns out that many of the same indicators of health that flow
in human blood are also present in sweat. The U.S. military
project aims to develop
skin "biosensors " that track what is flowing in the sweat of
soldiers, to monitor their health and improve their performance.
The high-tech devices, which look and feel like adhesive
bandages, could be used to collect real-time measurements, such
as heart rate, respiration rate and hydration, the researchers
said.

"It's getting away from the concept of, you go to the hospital,
they take a 10-milliliter vial of blood and a couple of hours or
days later come back with the answer," said Josh Hagen, a
chemical engineer for the Air Force Research Laboratory's 711th
Human Performance Wing at the Wright-Patterson Air Force Base
near Dayton, Ohio. [ Bionic
Humans: Top 10 Technologies ]

The sensors — flat, electronic chips that are embedded into
bandages — are designed to
record health information that can be downloaded onto
smartphones and computers. The military wants to use this
technology to learn how best to deploy its soldiers and how to
keep them functioning at peak performance.

Blood and sweat

Researchers at the Air Force Research Lab (AFRL) started mulling
the idea in 2009, when Morley Stone, the chief scientist of the
711th Human Performance Wing, shared a picture of a transdermal
patch — an adhesive patch that delivers drugs to the bloodstream
— and suggested they use a similar device to monitor more details
about the body.

Vital signs are important, but the AFRL is also interested in
looking at
biomarkers that indicate stress or fatigue, Hagen told Live
Science. These biomarkers could include measurements of dopamine
(a chemical in the brain associated with pleasure), cortisol (a
stress hormone) or other potential biomarkers. These chemicals
and hormones are well studied in the blood, but how they appear
in sweat is not as well understood.

A breakthrough came in 2008, when Esther Sternberg, a former
researcher at the National Institutes of Health who is now the
research director for the Arizona Center for Integrative Medicine
at the University of Arizona in Tucson, led a study on sweat
biomarkers that can be used to indicate depression. She
discovered that the biomarkers could be found in sweat at almost
identical concentrations as found in blood.

Hagen recalled that, after reading the paper, he pulled out a
1954 journal article about the chemical composition of sweat,
which suggested that anything found in blood that can dissolve in
water will show up in equivalent concentrations in sweat.
Researchers at the AFRL decided to test the concept.

Wearability

The first challenge was to make the sensors small enough to wear,
the researchers said. Transistors can be tiny these days, making
them easy to place on a soldier's body. The AFRL is integrating
the electronics into materials already designed with "skin
wearability" in mind, such as Band-Aids.

The key is to make the silicon-based electronic chips
interchangeable, based on what needs to be measured. Each sensor
should be able to look for specific biomarkers in sweat, but
prototypes could include multiple sensors, depending on what is
required, Hagen said.

The small bandage could be placed somewhere on the body —
figuring out where the sensors work best will be part of tests
scheduled for next year. The testing phase will
measure electrolytes, which the body excretes in sweat,
giving indications of a person's hydration level. Electrolytes
are detectable in sweat at a threshold that is higher than other
potential biomarkers, which makes them a good test case, Hagen
said.

So far, the project is expected to cost millions of dollars. But
once working biosensor prototypes are available, the military
wants to make the technology available for civilian applications,
in order to make individual units more affordable, the
researchers said.

The benefits for civilians could be groundbreaking, Hagen said.
Athletes could monitor their performance in real time to meet
workout goals, while children or people who are afraid of needles
could use these biosensors to glean information normally obtained
through blood tests, the researchers said.